docs(readme): update changelogs for v1.15.3

 - update gem list, changelog, and helm command for v1.15.3

Signed-off-by: Anton Ouzounov <[email protected]>

Author: Anton Ouzounov

CHANGELOG.md

@@ -1,5 +1,27 @@
 # CHANGELOG
 
+## [v1.15.3](https://github.com/vmware/kube-fluentd-operator/releases/tag/v1.15.3)
+
+#### Core:
+  -  chore(fluentd): upgrade fluentd v1.14.0 and gems #250 (@Cryptophobia)
+  -  chore(go.mod): upgrade k8s.io packages to v0.21.4 #248 (@Cryptophobia)
+  -  chore(ruby): upgrade to ruby version 2.7.4 #251 (@Cryptophobia)
+  -  docs(readme): update changelogs for v1.15.2 #242 (@Cryptophobia)
+  -  docs(repo): missing namespace in annotate cmd #244 (@brunowego)
+  -  chore(gems): upgrade json to 2.5.1 #254 (@Cryptophobia)
+  -  feat(context): propagate context from main func #256 (@Cryptophobia)
+
+#### Plugins:
+  -  chore(plugins): upgrade fluentd plugin gems #252 (@Cryptophobia)
+  -  chore(conf): upgrade systemd fluentd configs #257 (@Cryptophobia)
+  -  chore(plugins): upgrade kubernetes metadata plugin #258 (@Cryptophobia)
+
+#### Helm:
+  - None
+
+#### CI:
+  - None
+
 ## [v1.15.2](https://github.com/vmware/kube-fluentd-operator/releases/tag/v1.15.2)
 
 #### Core:

README.md

@@ -22,18 +22,18 @@ The easiest way to get started is using the Helm chart. Official images are not
 git clone [email protected]:vmware/kube-fluentd-operator.git
 helm install kfo ./kube-fluentd-operator/charts/log-router \
   --set rbac.create=true \
-  --set image.tag=v1.15.2 \
+  --set image.tag=v1.15.3 \
   --set image.repository=vmware/kube-fluentd-operator
 ```
 
 Alternatively, deploy the Helm chart from a Github release:
 
 ```bash
-CHART_URL='https://github.com/vmware/kube-fluentd-operator/releases/download/v1.15.2/log-router-0.4.0.tgz'
+CHART_URL='https://github.com/vmware/kube-fluentd-operator/releases/download/v1.15.3/log-router-0.4.0.tgz'
 
 helm install kfo ${CHART_URL} \
   --set rbac.create=true \
-  --set image.tag=v1.15.2 \
+  --set image.tag=v1.15.3 \
   --set image.repository=vmware/kube-fluentd-operator
 ```
 
@@ -544,7 +544,7 @@ This projects tries to keep up with major releases for [Fluentd docker image](ht
 | 1.13.0                     | 1.15.0                  |
 | 1.13.1                     | 1.15.1                  |
 | 1.13.3                     | 1.15.2                  |
-| 1.14.0                     | 1.15.3 (TBA)            |
+| 1.14.0                     | 1.15.3                  |
 
 ## Plugins in latest release (1.15.3)